sql_variant: Create an sql translator

In sctyner/dplyr050: A Grammar of Data Manipulation

Description

When creating a package that maps to a new SQL based src, you'll often want to provide some additional mappings from common R commands to the commands that your tbl provides. These three functions make that easy.

Usage

sql_variant(scalar = sql_translator(), aggregate = sql_translator(),
  window = sql_translator())

sql_translator(..., .funs = list(), .parent = new.env(parent = emptyenv()))

sql_infix(f)

sql_prefix(f, n = NULL)

sql_not_supported(f)

'base_scalar'

'base_agg'

'base_win'

'base_no_win'

Arguments

scalar, aggregate, window	The three families of functions than an SQL variant can supply.
..., .funs	named functions, used to add custom converters from standard R functions to sql functions. Specify individually in ..., or provide a list of .funs
.parent	the sql variant that this variant should inherit from. Defaults to base_sql which provides a standard set of mappings for the most common operators and functions.
f	the name of the sql function as a string
n	for sql_infix, an optional number of arguments to expect. Will signal error if not correct.

Helper functions

sql_infix and sql_prefix create default SQL infix and prefix functions given the name of the SQL function. They don't perform any input checking, but do correctly escape their input, and are useful for quickly providing default wrappers for a new SQL variant.

See Also

sql for an example of a more customised sql conversion function.

Examples

# An example of adding some mappings for the statistical functions that
# postgresql provides: http://bit.ly/K5EdTn

postgres_agg <- sql_translator(.parent = base_agg,
  cor = sql_prefix("corr"),
  cov = sql_prefix("covar_samp"),
  sd =  sql_prefix("stddev_samp"),
  var = sql_prefix("var_samp")
)
postgres_var <- sql_variant(
  base_scalar,
  postgres_agg
)

translate_sql(cor(x, y), variant = postgres_var)
translate_sql(sd(income / years), variant = postgres_var)

# Any functions not explicitly listed in the converter will be translated
# to sql as is, so you don't need to convert all functions.
translate_sql(regr_intercept(y, x), variant = postgres_var)

sctyner/dplyr050 documentation built on May 17, 2019, 2:22 p.m.